Chromium coated papermaking wire



April 6, 1965 OL ET'AL 3,177,113

CHROMIUM COATED PAPERMAKING WIRE Filed Aug. 27, 1963 INVENTORS MARTIN A,LDEN JOHN I.VL SAK BY Vii/40W ATTORNEY United States Patent G Filed Aug.27, 1963, Ser. No. 304,869 8 Claims. (Cl. 162-348) The present inventionrelates to metal wires for use on papermaking machines and it morespecifically resides in such a wire coated with chromium to enhance itsdurability and utility.-

Continuous, foraminous metallic belts, or wires? are used on papermakingmachines of various types, including Fourdrinier machines. cylindermachines. inver-form machines, verti-form machines and others. Wiresmost commonly used today are woven wire fabrics. although foraminoussheets are also being developed. The metals commonly 'used for thestrands of such wires are Phosphor bronze, bronze, brass, stainlessstecl'and others. The wire is the most important single part of thepapermaking machine, since the paper web is formed from a suspension ofpaper fibers in liquid on and by virtue of the wire. In the Fourdriniermachine this is accomplished by depositing the suspension of paperfibers from a head box onto the rapidly moving wire. which permits themoisture to drain through its interstices leaving a web of paper on the'wire to be delivered bythe wire to the first press part of the machine.Drainage and formation of the web is accelerated by table rolls andsuction boxes, over which the wire slides, so that the driest possiblepaper web is presented to the press part, which presses more moisturefrom the web before the web is passed through a drier part of themachine. Papers of good uniform quality can be etiiciently produced onlyif the wire is itself smooth and uniform, and provides maximum drainagethrough its interstices.

However. many forces and conditions are constantly at work todeteriorate the wires rapidly. requiring frequent replacement with theattendant high cost of replacement of the wires and shutdown of themachine. The high speed travel of the continuous wire about the rolls ofthe machine causes rapid flexing of the wire, resulting. if the wire istoo stiff. in premature fatigue failures. that is. failures due'tofatigue while the wireis otherwise still usable. Hence. flexibility isan important characteristic of a good Fourdrinier wire. Sliding of thewire'over the suction boxes and table rolls abrades the surface of thewire, making resistance to abrasion an important property of aFourdrinier wire. processes used. Fourdrinier wires are subjected tomore or less corrosive solutions that pit the surface of, and ultimatelyconsume the wire. Hence. resistance to corrosion is a necessaryattribute of a Fourdrinier wire. must resist deformation which mayresult from lumps in the stock and which leave marks and irregularitiesin the web. The wire must be made of a hard metal. sothat it will retainits shape and smoothness, so as not to snag paper fibers that will clogits interstices and impede drainage. It must also have a high tensilestrength to withstand stress even after substantial deterioration.

Research has been and is carried on continuously in an effort to improvethe characteristics of Fourdrinier wires and much-progress has beenmade. New metals and coatings have been developed to improve wires.However, changes in papermaking machines and processes make new demandson the delicate wires so that the life of a wire, in some applications,continues to be as short as a few days. The suggestion that Fourdrinierwires be coated with chromium was pursued, but experience establis hedthat the chromium coating made the Fourdrinier wire so brittle as tocause premature fatigue failures. ren- Depending upon the papermakingThe wire I 3,177,113 Ice Patented Apr. 6, 1965 dcring the protectivecapabilities of the chromium coating useless. However, the presentinvention provides a chromium coated Fourdrinier wire that is notsubject to premature fatigue failures. In addition, the presentinvention provides a Fourdrinier wire of greatly enhanced wear qualitieswithout materially increased stiffness by electroplating a wovenFourdrinier wire so that the surfaces subjected to wear have a thickerand harder coating of chromium, while the other surfaces have a coatingof lesser thickness and hardness.

However, a wire made according to the present invention also manifests anumber of hitherto wholly unexpected advantages. resulting in asurprisingly superior Fourdrinicr wire. For example, it was discoveredthat even after the chromium coating was abraded through and the exposedwire strands corroded from under the chromium coating. the coatingcontinued to support the strand and the wire displayed twice theabrasion resistance of an uncoated wire. The tensile strength of thestrands was found to be substantially increased. Where fissures in thechromium coating occur, exposing the strand, the strand manifests abouttwice the resistance to corrosion as would be expected and as wasexperienced with other coatings, such as nickel. Worn strands of otherFourdrinier wires develop burs projecting outward along the edges of theworn surfaces, and these burs catch fibers, clogging the interstices ofthe wire and reducing drainage. The chromium coated wires of the presentinvention, it was discovered, did not form burs, but wore smoothly.

Accordingly, it is an object of the present invention to provide achromium coated papermaking wire that is not subject to prematurefatigue failures.

It is another object of the present invention to provide a papermakingwire having great resistance to abrasion.

It is another object of the present invention to provide a papermakingwire that is highly corrosion resistant.

It is another object of the present invention to provide a papermakingwire having improved hardness.

It is another object of the present invention to provide a papermakingwire that retains a smooth surface throughout its use.

It is another object of the present invention to provide a papermakingwire that resists the formation of a sulfide scale.

It is another object of the present invention to provide a papermakingwire that resists the adherence of pitch on the surface of the strandsto require cleaning.

It is another object of the present invention to provide a papermakingwire that resists formation of a scale of paper coatings, such asaluminum resinate, on its surface.

It is another object of the present invention to provide a papermakingwire that is particularly well adapted for use in making such papers asphotographic or facsimile papers that are sensitive to cationic ormetallic contamination.

It is another object of the present invention to provide a papermakingwire that resists deformation.

The foregoing and other objects will appear in the description tofollow. In the description, reference is made to .the accompanyingdrawing which forms a part hereof and in which there is shown by way ofillustration a specific embodiment in which this invention may bepracticed. This embodiment will be described in sufiicient detail toenable those skilled in the art to practice this invention, but it is tobe understood that other embodiments of the invention may be used andthat structural changes may be made in the embodiment described withoutdeparting from the scope of the invention. Consequently, the followingdetailed description is not to be taken in-a limiting sense; instead,the scope of the present invention is best defined by the appendedclaims.

In the drawings:

FIG. 1 illustrates a papermaking wire embodying the present inventionmounted on a Fourdrinier papermaking machine,

FIG. 2 is a portion of the wire shown in FIG. 1 taken in section alongthe line 22 in FIG. 1,

FIG. 3 is a portion of the wire shown in FIG. 1 taken in section alongthe line 3-3 in FIG. 1.

Refering now specifically to the drawings, in FIG. 1 a

Fourdrinier wire 1 of the present invention is shown' mounted on adiagrammatic representation of a Fourdrinier papermaking machine so asto illustrate more clearly the use of this product and its advantages.However, it is not to be inferred from this specfic embodiment for useon Fourdrinier machines that the invention is limited specifically toFourdrinier wires. On the contrary, the present invention relates to allpapermaking wires for all types of machines and its embodiment inFourdrinier wires is but a single, though important, application of thepresent invention. Beginning at the left side of FIG. 1, the Fourdrinierwire 1 passes over a breast roll 2 as it moves in a clockwise direction;next the Fourdrinier wire 1 passes over a plurality of table rolls 3;then it slides over a plurality of suction boxes 4, and about a couchroll 5; then it moves to the left under a stretch roll 6, over a guideroll 7 and under a return roll 7a, and back to the breast roll 2.Frequently only the couch roll is driven and the table rolls 3, thebreast roll 2, the stretch roll 6, guide roll 7 and the return rolls 7aare idlers, although in some applications other rolls may also bedriven.

The paper fiber suspension (not shown) is fed on the top, or papermakingside 8, of the Fourdrinier wire 1 just above the breast roll 2 from acontainer known as a head box (notshown). The wire travels at a highrate of speed carrying the wet pulp over the table rolls 3 which aid inthe removal of the water from the pulp through the interstices of theFourdrinier wire 1. By this time the pulp has developed into a thin, wetweb of fibers (not shown), and as it passes over the suction boxes 4 thevacuum in the boxes 4 draws more of the moisture from the web and matsthe fibers, so that it is a well defined continuous web (not shown) bythe time it .reaches the couch roll 5, which in some applications is asuction roll; From the couch roll 5, the web is usually picked up on afelt (not shown) and drawn through the first press part (not shown) ofthe papermaking machine. In some applications, a Fourdrinier wire 1 maybe subjected to further strains by the use of a deflector blade (notshown) which scrapes against the underside, or suction box side 9 of thewire, and

o v.) sometimes machlnes are provided with shake mechanisms '(not shown)which will oscillate the wire 1 near the breast roll 2 to help disbursethe suspended fibers on the wire.

FIG. 2 illustrates a small portion of the wire 1 shown in FIG. 1 takenalong the line 2-2, and FIG. 3 illustrates a small portion of the wire 1in section, taken along the line 3-3 in FIG. 1. In the Fourdriniermachine the upper side of the wire 1 is subject to little, if any, wearand this will be referred to as the papermaking side 8. However the'lower. side of the wire 1 is subjected to a great deal of wear and willbe called the suction box side 9. In some types of machines, the wearside of the wire may be the papermaking side, and in other applicationsthere may be a wear side of the wire, but neither a papermaking side nora suction box side, properly speaking. In FIG. 2 a single weft strand 10is shown in section extending horizontally across the page and aplurality of warp strands 11 are shown above and beneath the weft strand10. In FIG. 3, a single warp strand 11 is illustrated in sectionextending across the page with a plurality of weft strands 10 above andbeneath the warp itrand 11. Phosphor-bronze cores 12 of the weft strands[0 are illustrated with coatings of chromium 13 about iheir surfaces,but frequently brass weft strands 10 are also used. Similarly, the warpstrands 11 have Phosphorbronze cores 14 with chromium coatings 15 abouttheir surfaces. About the knuckles 16 of the weft strand 10 in FIG. 2reed dents 17 are formed. These reed dents 17 are entirely covered bythe chromium coating 13 as are all other surface deformities which mightoccur in the strands 10 or 11.

In the drawing, the thicknesses of the chromium. coatings 13 and 15relative to the size of the cores 12 and 14 are greatly exaggerated inorder that the structure of the present invention might be more clearlyshown. In practice, the core strands 12 and 14 may be of diametersranging from 0.016 to 0.003 inch (a twisted cable, as dis tinguishedfrom the solid cores shown here, might have an outer diameter as greatas 0.032 inch, but its individual strands would be within the rangeindicated), and as will be brought out in greater detail later thethickness of the coatings 13 and 15 will be less than 0.001 inch. Hence,

' if these wire strands l0 and 11 were drawn to scale, the

coatings 13 and 15 would have thickness little greater than that of 'apencil mark.

It is to be noted that the chromium coating 13 about the weft strand 10is substantially thicker on the suction box side 9 of the wire 1 than onthe papermaking side 8, except at the interfaces between the ,weftstrand 10 and the warp strand llwhere the chromium coatings 13 and 15are both extremely thin. Also, the chromium coating 15 about the warpstrands 11 is substantially thicker on the suction box side 9 of thewire 1 than on the papermaking side 8, except at the interface betweenstrands 10 and 11.

Wires embodying the present invention are made in the following manner.First, strands of any of the commonly used alloys or metals are woventogether in the usual way, except, of course, in those cases where thewire is made of a foraminous sheet. electroplated with chromium to thedimensions disclosed herein. As a result, the coating at the interfacesof the crossing strands 10 and 11, where there is no wear, is at aminimum. Hence, flexibility is promoted without loss of abrasionresistance. Also, stress points and other deformities, such as reeddents 17, which have had greater vulnerability to corrosion, arecovered.

The mentioned differential in thickness of the coating 13 and 15 betweenthe papermaking side 8 and the suction box side 9 is maintained toensure maximum strengthening of the wire 1 against wear of various sortswith a minimum loss of necessary flexibility to avoid'premature fatiguefailure. In. commercial embodiments, the thickness of the coating 13 and15 on the suction box and papermaking sides 9 and 8, respectively, areon the order of 0.0001 inch and 0.00005 inch, and although an absolutecommercial standard has not been fixed, a tentative standard of 0.000070inch on the suction box side 9 and 0.000049 inch on the papermaking side8 is now in practice. Hence, it may be said that the differential inthickness of the chromium coating 13 and 15 between the suction box side9 and the papermaking side 8, respectively, should be between aboutone-and-one-half and two to one. Experiments indicate that successfulwires could be made having chromium coatings 13 and 15 of thicknesseswithin a range of 0.000025 to 0.00075 inch on the suction box side 9 anda range of 0.0000125 to 0.0003 on the papermaking side with the aboveindicated or greater differential in thickness being maintained betweenthe coatings 13 and 15 on the two sides 8 and 9, the thinnest coatingbeing that necessary to continuity of the coating, and the thickestdimension being that allowable on one side of the wire 1 without causingpremature fatigue failures. Those extremes, as a practical matter, areof limited application due to the great difference in stress, abrasion,corrosion, etc., to which wires 1 are subjected in different papermakingmachines and mills. Hence, commercially acceptable dimensions lie wellwithin the extreme limits established under controlled conditions. asthe coating 13 and 15 on the suction box side 9 of the The endless metalbelt is then Moreover, just wire 1 may be made thicker by reducing thethickness of the coating 13 and on the papermaktng side 8 of the wire 1while preserving maximum flexibility, the results are further improvedby providing a more ductile coating- 13 and 15 on the papermaking side 8of the wire 1 where hardness is not necessary, and a harder coating 13and 15 and the environment within which they are used. These wires maybe up to 350 inches wide and .over 400 feet long. The mesh count of thewire may exceed 100. although a mesh count of 75 is common. There arevarious types of weaves used in papermaking wire, such as a plain,semitwill and full twill, but most commonly a semi-twill weave is used.The normal life of a wire may vary from only a few days to a month and ahalf, or more. The speed of the movement of the wire on a machine may beas high as 4000 feet per minute.

Great care must be exercised in changing the wires on a Fourdriniermachine so as not to introduce ridges or kinks in the wire, renderingthe wire useless or substantially weakening it. During the changes ofthe Fourdrinier wire, the machine of course must be shut down, andspecial equipment and a trained crew of men is required to change thewires on the machine. The shutdown time of a machine for a wire changemay vary from as little as one hour to over twelve hours, but in anyevent changing wire on a machine is very expensive in terms of the costof the wire, the cost of the labor involved and the cost of the lostproduction as a result of the shutdown time. Hence, the life of the wireis a very important economic factor in the production of paper.

The following table provides test data of actual wires 1 made accordingto the present invention and experimentally used on differentpapermaking machines in production of paper. The wire life varies frommachine to machine depending upon the corrosiveness of the pulpsuspension used, the type of machine used, the speed at which themachine was operated, etc. The length of life shown is measured in 24hour operating days. hand column is a figure representing the averagelife of uncoated wires, and in the right hand column is the life of awire 1 which was coated with chromium according to the presentinvention.

Average Lite Average Lite ofan t'ncoatcd of (hrtuniitm Wire, daysFnnrtlrinim i \l'irc. days 25 l 33 '15 4'2 (i4 ll? 20 'll 40 (i0 11% 42mg at) it! 54 10. 7 i 42 On the basis of data thus far collectedcomparing wires 1 coated according to the present invention withconventional uncoated wires, it may be asserted as a generalization thatan undamaged wire Icoated according to the present invention will have alife of at least one and a half times a conventional unconted wire. Inaddition to the remarkably enhanced life of the wire 1, wires 1 coatedaccording to the present invention, unexpectedly, wore smoothly and didnot form radially extending burs, as do the conventional. uncoatedwires. These burs formed on the uncoated wires tend to collect pitch andpulp fibers, clogging the interstices of the wire 1 and preventing Inthe left proper drainage. When this occurs it is necessary to shut downthe mcahine and clean the wire with either an acid or a caustic.solution or an organic solvent such as kerosene depending upon thecircumstances of the situation. However, since the wires 1 madeaccording to the present invention wear smoothly, the need to clean thewires 1 is obtained.

The remarkable improvement in the life of the wires coated according tothe present invention stems from several unexpected results encounteredonly after actual application of the wire 1. It has been the experiencewith previous wire coated with different materials, that where a fissureor pin hole developed in the coating exposing the core, a point of highvulnerability to corrosion of the core strand was developed. Theopposite result obtained I by the use of chromium coating according tothe present invention. Contrary to all expectations the core wire, whereexposed either by pin holes, fissures or wear phase in the chromiumcoating actually exhibited greater resistance to corrosion than anuncoated strand. Also, the tensile strength of the wire 1 embodying thepresent invention is measurably increased. The ability of the chromiumcoating to continue to withstand wear even after it wears through at itsbottommost surface, and even after a portion of the core is eroded awaypresented surprising improvement in the life of the wire.

We claim:

1. An endless wire papermaking fabric having a wear side and a sideopposite said wear side, the combination comprising: warp strands andweft strands, woven together to present opposing interfaces to eachother where said strands cross, and having metallic cores with achromium coating; said chromium coating on said wear side of said wirehaving thickness in the range of 0.000025 to 0.00075 inch, and on saidopposite side of said wire having thickness in the range of 0.0000125 to0.0003 inch; and

i said chromium coating being thinnest on said interfaces.

2. In an endless wire for a papermaking machine, the combinationcomprising: a plurality of weft strands and a plurality of warp strandswoven together and presenting interfaces at their intersections; saidwire having a wear side and a side opposite said wear side; said strandshaving metallic cores and a chromium coating between 0.0000125 and0.00076 inch thick enclosing said cores except at said interfaces; saidchromium coating on said wear side being from approximatelyone-and-one-half times to six times as thick as said chromium coating onsaid opposite side and being thinnest on said interfaces.

3. A papermaking wire having a wear side and an opposite side to saidwear side, and being comprised of a metallic core; and a chromiumcoating enclosing said core and being of varying thickness in the rangeof 0.0000125 inch and 0.00075 inch; said chromium coating beingapproximately one-and-one-half times to twice as thick on said wear sideas on said opposite side.

4. A papermaking wire for a Fourdrinier machine composing thecombination of Phosphor-bronze warp strands woven together with metallicweft strands, said strands forming interfaces at points of contact; anelectrodeposited chromium coating enclosing said strands and varying inthickness within the range of 0.0000125 inch to 0.00075 inch except atsaid interfaces; said wire having a papermaking side and a suction boxside; said chromium coating on said suction box side being approximatelyoneand-one-half times as thick as said chromium coating on saidpapermaking side of said Wire.

5. In a papermaking wire the combination comprising: a metallic corestructure; a chromium coating enclosing said core in varying thicknessesbetween 0.0000125 inch and 0.00075 inch; at least one side of said wirebeing a wear side; said chromium coating on said wear side being harderand thicker than said coating elsewhere on said wire.

6. A wire for papermaking comprising: a plurality of lengthwise copperbase metallic wires and a plurality of 7 transverse copper base metallicwires woven with the respective wires crossing overand under one anotherin a repeated pattern to form a fabric having a papermaking side and awcarsidc opposite therefrom; the respective wires bearing against oneanother on their interfaces at the points of crossover and formingknuckles that constitute a wear surface for the wear side and asupporting surface for the 'papermaking side; and a thin chromium filmcoating said fabric that is thickest on the wear surface andprogressively thinnerhtoward the supporting surface.

7. A papermaking wire comprising the combination of a foraminous metalbelt having a wear side for receiving a preponderance of abrasive wearin use, and an opposite side for receiving substantially less abrasivewear in normal use of said belt;

and a chromium coating enclosing said foraminous belt, 'having asubstantially uniform thickness of about 0.0001 inch on said wear sideof said belt, and having a substantially uniform thickness of 0.00005inch on said opposite side of said belt.

8 1 8. Apapcrmaking wire comprising the combination of a foramainousmetal belt having a suction box side and a papermaking side; and achromium coating ofsubstantially uniform thicknesses on each side of thebelt, each thickness being in a range no greater than about 0.0001'inch;said chromium coating on said suction box side of said belt being aboutone-and-one-half to two times as thick as said coating on saidpapermaking side of said wire. 1

References Cited by the Examiner UNITED STATES PATENTS DON A. WAITE,Primary Examiner. V

5. IN A PAPERMAKING WIRE THE COMBINATION COMPRISING: A METALLIC CORESTRUCTURE; A CHROMIUM COATING ENCLOSING SAID CORE IN VARYING THICKNESSESBETWEEN 0.0000125 INXH AND 0.00075 INCH; AT LEAST ONE SIDE OF SAID WIREBEING A WEAR SIDE; SAID CHROMIUM COATING ON SAID WEAR SIDE BEING AHARDER AND THICKER THAN SAID COATING ELSEWHERE ON SAID WIRE.